(1) Field of the Invention
This invention relates to a side well for a metal melting furnace. More particularly, the invention relates to a side well that may be used as a metal melter and/or a metal agitator or metal stirring pump.
(2) Description of the Related Art
Metals are frequently melted in metal melting furnaces. For example, relatively clean aluminum and copper scrap materials, as well as pure metals, are usually melted in reverberatory furnaces for eventual use or re-use by metal fabricators. A direct charge reverberatory furnace (DCF) heats the furnace contents both by direct flame and by radiation from hot refractory linings and possibly from additional heating elements. At its simplest, such a furnace is a steel box lined with alumina or other refractory brick having a flue at one end and a generally vertically lifting door at the other end closing a main entrance for the furnace through which a metal is directly charged into the furnace. The charge of molten metal may be introduced through the main entrance and lies in a shallow hearth having a relatively low roof so that flame passes across the surface of the charge. Conventional oil or gas burners are usually placed on either side of the furnace to heat the refractory lining and to melt the metal. The resulting molten metal is then poured into a casting machine to produce metal ingot.
A static furnace may be tapped at the bottom by simply removing a ceramic-covered plug which then allows the molten aluminum to flow into a launder and from there to the casting machine. Direct charge furnaces tend to be fully drained on a periodic basis, although restarting such furnaces after they have been fully drained can lead to problems from residual metal that has solidified in areas that cooled too quickly. Therefore, such furnaces are not normally provided with auxiliary equipment, such as side wells, where metal may linger and solidify during draining. When agitation of the metal in the furnace is required, it is often done by electromagnetic stirring devices that are positioned on the outside of the furnace wall without direct metal contact. Such furnaces are generally unsuitable for melting light gauge metal (e.g. metal foil) or finely divided metal (metal powders) because the large surface area of the metal allows a substantial amount of oxidation to take place before the metal is fully melted in the main furnace chamber. There can therefore be significant metal loss.
In contrast, recycle reverberatory furnaces (RF) are used more frequently for contaminated scrap, e.g. scrap metal coated with organic materials, and are provided with one or more side wells where the coated scrap is mixed with a flux that enables contaminants to be skimmed off as a floating dross before the molten metal enters the main chamber of the furnace from the side well. Such furnaces may also be used for melting light gauge metal scrap, shredded scrap and metal powders because the flux can isolate the metal from an oxidizing atmosphere as the metal is melted. Furnaces of this kind tend to operate continuously and are never completely drained, so there are no problems of furnace start-up, even though the side wells may provide areas where molten metal may linger. However, the side wells are relatively large structures that must provide settling space and areas for the addition of flux, therefore increasing capital costs and the need for substantial amounts of floor space.
Although, as stated, direct charge furnaces are not generally provided with side wells, an electromagnetic pumping system is known for such furnaces that employs a linear motor to withdraw molten metal from a furnace through a channel to a separate chamber or charge well and then return it through a further channel to the furnace. However, electromagnetic pumping systems are expensive and can be bulky and complex. Also, they may not avoid the problem of metal solidification during furnace draining.
U.S. patent application publication no. US 2007/0108674 A1, published on May 17, 2007, to Yu et al. discloses a scrap melter for light gauge scrap having a shrouded impeller which is immersed in a molten metal pool in a charge bay or furnace. It is inclined at an angle relative to the vertical to create a vortex forming a whirlpool at the surface of the molten metal. The center of the whirlpool is horizontally displaced from the so that scrap can be charged into the whirlpool to be ingested into the vortex.
U.S. Pat. No. 6,074,455 issued on Jun. 13, 2000 to van Linden et al. discloses a method of melting floatable scrap in which molten metal is fed through two melting bays, a first one of which is provided with a rotatable impeller. The molten metal is introduced into the first melting bay from below and is rotated to form a vortex.
U.S. Pat. No. 4,940,214 issued on Jul. 10, 1990 to Gillespie discloses a furnace having a charging well for the introduction of light weight solid scrap. A vortex generator including an impeller imparts a vortex to the melt in the well. An elevating mechanism makes it possible to elevate and remove the impeller.
U.S. Pat. No. 4,286,985 issued on Sep. 1, 1981 to van Linden et al. provides a receptacle supplied with molten metal that creates a free vortex. A pump is used to supply the molten metal to the receptacle. Metal scrap may be introduced into the receptacle so that it is ingested by the vortex.